This invention relates to a process for recovering unsymmetrical dimethyl hydrazine (UDMH). More specifically, pure UDMH is recovered from a solution of UDMH, water, and other volatiles and non-volatiles by adding a distillation agent to the solution.
It is important to note that the three amine fuels, UDMH, monomethylhydrazine, and anhydrous hydrazine are each very dissimiliar materials. The hydrazines are so named because of the nitrogen bonding within the molecule. The differences between the three hydrazines are attributable primarily to either the absence of or presence of one or two carbon atoms with bonds to adjacent hydrogen atoms. Unsymmetrical dimethyl hydrazine does not form an azeotrope with water while both of the other materials do form these azeotropes. There are numerous techniques available for dehydration of the azeotrope called hydrazine hydrate. U.S. Pat. Nos. 2,963,407 and 2,698,286 teach these techniques. In one case various alcohols are added to break the azeotrope form by allowing water to migrate up to the top of the column from where it can be removed as overhead product. In the other case, materials such as analine are used in order to break the azeotrope. The difference between the dehydration techniques employed for anhydrous hydrazine and monomethylhydrazine are slight even though the major difference between these materials is that in one case for hydrazine there is a purely inorganic compound, while in the case of monomethylhydrazine there are carbon and hydrogen atoms involved within the molecule. In the case of separation by addition of a alcohol, the water is removed from the azeotrope by taking it up the column and removing water/alcohol as a product. This situation does not occur in the case of UDMH. The isopropanol treated within the present invention is utilized as a means for isolation between the water and UDMH thereby keeping both the water and the isopropanol in the distillation pot. Since unsymmetrical dimethyl hydrazine does not form an azeotrope but only has an affinity for water (as evidenced by a pinch point at the low concentrations of UDMH in water) it is necessary to treat UDMH differently as it really behaves differently than the other hydrazines. The use of isopropanol in U.S. Pat. No. 2,936,407 is only in the case where the alcohol passes up the column, thus the alcohol serves an entirely different function within this invention.
Should an experimentor investigate the boiling points of UDMH water and isopropanol, he would find that isopropanol has a boiling point midway between the low boiling unsymmetrical dimethyl hydrazine and the higher boiling water. He would have found that this is not the case with respect to the materials treated in the aforementioned patents and would not have applied isopropanol within this context to the separation of UDMH and water.